Investigation of tail rotor cable of a helicopter

Tail rotor cables of a helicopter were sent to the laboratory for identifying the mode of failure. Visual, stereo-binocular and scanning electron microscopic examination revealed that the cables have failed by overload under tension. There were no major damages to the cables except for some bruise marks. These minor damages are normal during handling and/or usage, and they do not appear to have any bearing on the present failure. The breaking load of cable Nos. 9 and 13 were determined and it was found to be in the range 1100 to 1200 kg. It is believed that the cables got snapped due to sudden overload and the failure is secondary in nature. The reason for such high abnormal load on the cables needs to be established